1. Field of the Invention
The present invention relates to a developer scraping member for scraping developer from a developer carrying member, and a developing apparatus equipped with such developer scraping member.
2. Related Background Art
In the image forming apparatus such as a copying apparatus, a printer or a facsimile apparatus, there has conventionally been executed visualization of a latent image, formed on an image bearing body such as an electrophotographic photosensitive member or an electrostatic recording dielectric member, as a toner image by development with a developing portion.
As one of such developing portions, there have been proposed and commercialized various types of dry one-component developing portion. However any of these types has been associated with a difficulty in forming a thin layer of non-magnetic toner (non-magnetic one-component toner), which is the non-magnetic one-component developer, on the developer carrying member.
Nevertheless, in order to meet the currently desired improvements in the resolution and definition of the image, the development of the method for forming a thin toner layer and of the apparatus therefor is essential, and certain measures have therefore been proposed.
For example, the Japanese Patent Application Laid-Open No. 54-4303 discloses a method of abutting a metal or rubber elastic blade with a developing roller constituting a developer carrying member and causing the toner to pass between and to be regulated by the elastic blade and the developing roller thereby forming a thin layer of the toner on the developing roller and providing the toner with sufficient triboelectricity by the friction in the abutting portion.
In such method, if the non-magnetic toner is regulated by the elastic blade, there is required a separate toner feeding member for feeding the toner onto the developing roller. This is because the non-magnetic toner cannot be fed by magnetic force, though the magnetic toner can be fed onto the developing roller by the magnetic force of a magnet provided inside the developing roller.
In a developing portion disclosed in the Japanese Patent Application Laid-Open No. 58-116559, as shown in FIG. 8, in a developing container 102 containing non-magnetic one-component toner 106, a fur-brush-like roller (brush roller) 115 contacting a developing roller 103 is provided at an upstream position with respect to an elastic blade 104 in the rotating direction of the developing roller 130 in order to scrape off the residual toner not consumed in the image development but remaining on the developing roller 103 and to feed new toner 106 onto the developing roller 103.
It is thus rendered possible to satisfactorily form a thin layer of the non-magnetic toner 106 on the developing roller 103 and to satisfactorily develop the electrostatic latent image on a photosensitive drum 101, whereby a solid black image of a high density and a large area can be faithfully reproduced in the development to obtain a satisfactory image.
However, the above-described brush roller 115 is formed by planting fibers of nylon or rayon on a metal core, and, in a prolonged repeated use of the developing portion, the fibers become detached from the roller and clogged between the elastic blade and the developing roller, thereby generating a white line (streak) in such clogged portion, or the fibers are turned down on the roller to result in defective contact between the brush roller and the developing roller whereby the solid black image cannot be reproduced sufficiently because of deficient feeding and scraping of the toner.
Therefore, it is proposed to form the toner feeding member by an elastic roller with a foamed structure, composed of an open cell foamed member such as polyurethane foam of a relatively low hardness and to contact such roller with a low pressure to the developing roller, whereby the feeding of the toner onto the developing roller and the scraping of the residual toner therefrom are rendered possible by suitable surface irregularity (asperity) of the foamed member.
In such developing portion, however, since the elastic roller is composed of an open cell foamed member, the toner particles enter and gradually clog the cells of the elastic roller when the developing operation is repeated many times, particularly in case the toner of a small particle size is used under a high humidity environment or the toner is substantially spherical. When the toner clogging spreads over the entire foamed member of the elastic roller, it becomes harder to result in an excessively large contact pressure of the elastic roller on the developing roller, eventually leading to an increased driving torque of the developing roller and the elastic roller or unevenness in the coating and scraping of the toner by the elastic roller on the developing roller, whereby uneven coating is developed on the developing roller in the undesirable level.
In order to prevent the drawbacks resulting from such clogging with toner of the interior of the elastic roller, there can be conceived the following measures: (1) providing the surface of the elastic roller with a skin layer for preventing toner clogging; (2) constituting the elastic roller with a closed cell foamed member; and (3) using an open cell foamed member of a high density with as small cells as possible. These measures, however, result in the following drawbacks.
In the measure (1), when the skin layer of the elastic roller is maintained in contact with and rubs the surface of the developing roller, the skin layer has an excessively strong function of rubbing in the toner onto the developing roller, resulting in the fusion of the toner onto the developing roller or physical change of the toner, thereby causing deterioration of the toner and an increase in the fog level when the developing operation is repeated many times. Even if the surface of the skin layer is made appropriately coarse, it is locally harder than the surface of the foamed member, thus applying a locally high pressure on the toner and the developing roller, so that similar drawbacks cannot be avoided.
Also as the skin layer is formed very thin, it may be abraded or scraped off by the friction with the developing roller, whereby the toner particles still intrude the cells of the foamed member and there cannot be assured the stability in the prolonged use.
In the measure (2), the elastic roller can satisfactory execute coating and scraping of the toner on the developing roller as in the open cell foamed member, but the closed cell foamed member has a higher hardness and a higher repulse elasticity in comparison with the open cell foamed member so that the hardness of the elastic roller becomes excessively high. For this reason, if the elastic roller is so positioned as to be stably and securely contacted with the developing roller, the contact (abutting) pressure of the elastic roller becomes excessively high on the toner and the developing roller, resulting in various drawbacks such as an increased driving torque of the developing roller and the elastic roller and an increased fog level derived from the change of physical property (deterioration) of the toner after a prolonged use.
Such drawbacks may be avoided by reducing the hardness of the closed cell foamed member as far as possible, but, in such case, the foamed member inevitably contains a large amount of an oily component which oozes out and sticks to the developing roller and the toner when the elastic roller is left in contact with the developing roller and the toner over a prolonged period under a high temperature environment, whereby the toner is fused and sticks to the developing roller. With such fusion of the toner on the developing roller, the toner newly fed thereto is rubbed with the fused toner on the developing roller, whereby the appropriate triboelectricity cannot be obtained and a fog is undesirably generated by the deficient charging of the toner.
In the measure (3), in comparison with the open cell foamed member of an ordinary cell number, for example a foamed member with 30 to 50 cell/inch such as polyurethane foam, the open cell foamed member with finer cells such as 100 cell/inch or larger allows to prevent intrusion of the toner into the elastic roller in case of toner particles of irregular form to a certain extent, but is not very effective for the toner of substantially spherical shape. As a result, the hardness of the entire elastic roller becomes excessively high as in the case of measure (2), thus resulting in drawbacks such as an increase in the driving torque of the elastic roller and the developing roller, deterioration of the toner and an increased fog level derived from the toner deterioration.
An object of the present invention is to provide a developing scraping member capable of satisfactorily scraping the developing from the developing carrying member, and a developing apparatus provided with such developer scraping member.
Another object of the present invention is to provide a developer scraping member capable of satisfactorily scraping and feeding the toner on the developing roller by the elastic roller without excessive pressure on the developing roller and the toner thereon even after prolonged use of the elastic roller in the developing portion, thereby enabling satisfactory image development to provide a high quality image without fog and the like, and a developing apparatus provided with such developer scraping member.
Still another object of the present invention is to provide a developer scraping member for scraping developer from a developer carrying member, comprising:
a surface layer having a foamed member;
a base layer provided inside the surface layer; and
an intrusion preventing layer between the surface layer and the base layer, wherein the intrusion preventing layer prevents the developer from intruding into the surface layer from intruding into the base layer.
Still another object of the present invention is to provide a developing apparatus comprising:
a developer carrying member carrying developer; and
a developer scraping member for scraping developer from a developer carrying member, including:
a surface layer having a foamed member;
a base layer provided inside the surface layer; and
an intrusion preventing layer between the surface layer and the base layer, wherein the intrusion preventing layer prevents the developer intruded into the surface layer from intruding into the base layer.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following description which is to be taken in conjunction with the attached drawing.